The present invention relates to a process for determining the fuel flow into the gasifier occurring in the partial oxidation of solid fuels of fine grained and up to dust-like particle sizes.
In the partial oxidation of solid fuels such as lignite or coal or petroleum coke it is necessary to introduce the fine-grain or dust-like fuels together with the gaseous or vaporous reaction medium in a uniform and quantitatively exactly defined flow into the gasifier. The fuel particles may be reduced to the desired grain size by means of a preceding grinding device. The uniformity and exact control of the flow to the gasifier is necessary in order to obtain constant operating conditions in the gasifier which assure a uniform quality of the produced partial oxidation gas. The gaseous or vaporous reaction media used in these cases may be oxygen or air or oxygen-enriched air and possibly also steam. If the proportion of fuel in the reaction mixture in the gasifier is too low an undesirable increase in the operating temperature in the gasifier will occur because of too high a ratio of oxygen to fuel. On the other hand if the proportion of fuel in the reaction mixture for the gasifier is too high an unstable reaction of the fuel with the oxidizing agent will result. This may have the consequence that unreacted fuel particles become deposited in the gasifier or are passed out of the gasifier together with the generated gas. Besides, it is not impossible that a breakdown of the reaction occurs.
The volume flow of the gaseous or vaporous reaction medium into the gasifier can be determined in a comparatively easy and unproblematic manner by measurement of the effective pressure differential, for instance by way of gauge orifices.
Much more difficult, however, is the quantitative determination of the solid fuels. For instance, the so-called conveyor-type scales cannot be used since fine-grained and even dust-like solid fuels cannot readily be moved onto the conveyor lines and thus be subjected to measurements.
Likewise unfeasible are measuring methods which operate by the principle of a medium flowing onto a surface or which are based on the measurement of the impact energy of a stream of solid particles onto a movable bounce plate where the impact is obtained by a constant drop height. These methods are of questionable value in the present case because of the strongly erosive properties of the fine grained or dust-like solid fuels.
In the prior art the fuel was therefore usually introduced into the gasifier by means of a screw conveyor. This means that the quantitative dosage of the fuel was largely effected by regulating the rpm of the screw conveyor. This method, however, also has an inherent lack of exactness since the physical properties of the fuel, in particular its flow behavior and adhesion property, are subject to certain changes. This method in addition requires obviously the use of a screw conveyor. This is undesirable in present methods where the conveyance of the fuel to the gasifier is effected otherwise, for instance by pneumatic conveyance.
An attempt has also been made to determine the fuel prior to its entry into the gasifier by controlling and measuring the so-called blow pressure in the inlet duct of the gasifier, that is, measuring the flow-dependent pressure of the combined reaction media (gaseous or vaporous reaction medium plus fuel). This blow pressure is composed of the flow-dependent pressure loss within the inlet duct and the back pressure of the flame, in which case the latter constitutes a substantial fraction of the blow pressure. For this reason a sudden breakdown of the reaction, that is of the flame in the gasifier, causes immediately a corresponding drop of the blow pressure. There is also the point that the pressure within the gasifier is different upon commencement of the operation than during continuous operation. In case of the initial operation the blow pressure cannot be used to control the installation. This method therefore likewise cannot be considered as desirable.
The present invention, therefore, has the object to provide for a process for determining the fuel flow into the gasifier in case of the partial oxidation (gasification) of fine-grain or dust-like solid fuels and provide such method while avoiding the shortcomings of the prior art processes.